1. Field of the Invention
The present invention relates to a vehicle height control device which carries out vehicle height control satisfactorily when the ignition switch is turned off.
2. Description of the Prior Art
The function of a vehicle height control device is to maintain the vehicle height at a constant value, even though the load on the vehicle changes as passengers get in or out, and generally is constructed to control the vehicle height to be within a certain range by detecting the vehicle height, then lowering the vehicle body if the detected vehicle height exceeds a certain upper limit, and raising the vehicle body if the vehicle height falls below a certain lower level.
However, in order to carry out vehicle height control in this way, electric power is required to drive the vehicle height adjustment mechanism which raises and lowers the vehicle body, and therefore if vehicle height control is carried out when the engine is stopped and can not recharge the battery which forms the electric power supply for the vehicle, battery power will be consumed, and the engine may not be able to be restarted.
In answer to this, it has been conventionally proposed, for example in Japanese Utility Model Laying Open Publication Sho 61-64006 (1986), that in view of the fact that vehicle height control with the ignition off is likely to be required as passengers get out of the vehicle after the ignition is switched off, only the vehicle body lowering control which requires no electric power supply for the compressor system should be carried out within a fixed period, and once the fixed period has elapsed after the ignition is turned off, that the lowering control should also be stopped.
In the above prior art, however, the vehicle height control decision after the ignition switch is turned off is made using the same upper limit value as was used for the vehicle body lowering control while the ignition switch was turned on, so that the vehicle body is lowered as the vehicle height exceeds this limit when for example passengers get out of the vehicle, and the vehicle height is controlled so as not to exceed this upper limit. Therefore, when, after the control has stopped, the load on the vehicle body is increased as passengers get into the vehicle or goods are loaded, there is a problem that the vehicle sinks too low, and the vehicle body comes to rest on protrusions in the road surface such as curbstones, causing damage to the vehicle body.
Further, on the other hand, since the vehicle height control is carried out by raising and lowering the vehicle body according to variations in the vehicle height, if the vehicle height control is carried out while a passenger door or the trunk is open with the load on the vehicle being fluctuating, then vehicle height control will be carried out each time when the load on the vehicle body changes, and therefore the vehicle body will be raised and this unnecessary control, it has already been considered, as disclosed in for example Japanese Utility Model Publication Sho 62-9123 (1987), to suspend the execution of vehicle height control while a passenger door or the trunk is open.
In view of this it would be considered to combine these techniques in order to even further restrict the power consumption from the battery when the ignition switch is being off. In other words, by carrying out vehicle height control when the ignition switch is off for only a fixed period after the ignition switch is turned off, and also by suspending the vehicle height control after the ignition switch turn off if a door or the trunk is open so that power consumption due to unnecessary vehicle height control carried out while a door and/or the trunk is open can be restricted.
However, if the above techniques are simply combined, if a door or the trunk is left open for a long time, then vehicle height control may not be able to be carried out satisfactorily. In other words, if vehicle height control with the ignition switch being turned off is simply restricted to a fixed period after the ignition switch is turned off, if the door or the trunk is left open for a long time, then it may become impossible for the vehicle height control being carry out, or vehicle height control may be ended before it is completed, and it may not be possible for the vehicle height being adjusted to a target value after the ignition switch has been turned off.
In order to be able to carry out vehicle height control even when a door or the trunk is left open for a long time, it would be considered to lengthen the period after the ignition switch is turned off for which control is carried out, but if the control execution period is simply lengthened, it is no longer possible to achieve the original object of applying a time limit, that is to restrict the battery power consumption by making vehicle height control with the ignition switch off possible only for a period normally required for passengers to get out of the vehicle and so forth, and thus the power consumption due to the vehicle height control device would be increased.